One of the requirements for an ultra wide band (UWB) device is compliance with the spectrum mask mandated by spectrum regulators. In the United States, the spectrum mask is prescribed by the Federal Communication Commission (FCC). Other countries have similar regulators and may have their own requirements for spectrum masks.
Although the amplitude of signals which are transmitted should not exceed the spectrum masks, it is desirable for a transmit signal to efficiently use the permissible spectrum without violating the spectrum mask. Therefore, the spectrum of a signal that is being transmitted can be shaped, to more efficiently fill out the spectrum mask. There may be other reasons to utilize a particular amplitude for a signal, for example a particular type of device.
One way to shape the spectrum of a transmitted signal is to control the power of the transmitter in a transmission system utilizing an analog feedback loop. However, adjustments to the power provided to the transmission system cannot be effectively used to provide prompt control of the spectrum of a signal that is in the process of being transmitted, because of the closed loop feedback that is conventionally used in a transmission system.
In a transmission system having an analog feedback loop, power changes typically are detected and responded to gradually. The feedback loop is provided to compensate for changes in amplitude of the transmission signal, which are perceived as errors. The feedback loop tends to dampen changes in amplitude to the power.